This invention relates to catalyst systems for olefin polymerizations.
The use of fluorided alumina as a support material for Phillips-type chromium polymerization catalysts has been widely disclosed in the patent literature. The following U.S. Pat. Nos. (USP) relate to this technology: 5,221,720; 5,221,655; 5,221,654; 5,219,962; and 5,219,817 (all McDaniel et al, and all assigned to Phillips Petroleum Company). Similarly U.S. Pat. No. 4,100,337 (Noshay et al, assigned to Union Carbide Corporation) teaches the use of fluorided silica supports for chromium polymerization catalysts.
Halogenated catalyst supports are also known for use with other types of ethylene polymerization catalysts. For example, U.S. Pat. No. 4,536,484 (Lacombe et al, assigned to Atochem) teaches the preparation of a functionalized support (by the reaction of an organoaluminum compound with a functionalized magnesium compound) followed by the chlorination of the functionalized support. The resulting support is used with a Ziegler-Natta type catalyst and an aluminoxane cocatalyst.
Similarly, European patent application EP 906,920 (Saudemont et al, assigned to Elf Atochem) teaches the preparation of a functionalized support, followed by the fluorination of the functionalized support. The resulting support material allows the use of aluminum alkyls as active cocatalysts for metallocene catalysts. This is a desirable result as aluminum alkyls are less expensive than aluminoxanes. However, EP 906,920 also shows that directly fluorided supports (where xe2x80x9cdirectly fluoridedxe2x80x9d refers to supports which were not functionalized before being treated with a source of fluorine) do not provide catalytic activity when used with aluminum alkyls (see comparative example 25 of the ""920 application).
In contrast, we have now discovered that of a directly fluorided metal oxide provides an excellent support for a phosphinimine/aluminum olefin polymerization catalyst.
In one embodiment, the present invention provides a supported catalyst system for olefin polymerization comprising:
a) a directly fluorided metal oxide;
b) an aluminoxane; and
c) a catalyst which is a complex of a group 4 metal having at least one phosphinimine ligand.
The present invention also provides a process to prepare polyolefins using the catalyst technology of this invention.
The use of metal oxide supports in the preparation of olefin polymerization catalysts is known to those skilled in the art. An exemplary list of suitable metal oxides includes oxides of aluminum, silicon, zirconium, zinc and titanium. Alumina, silica and silica-alumina are metal oxides which are well known for use in olefin polymerization catalysts and are preferred for reasons of cost and convenience. Silica is particularly preferred.
It is preferred that the metal oxide have a particle size of from about 1 to about 200 microns. It is especially preferred that the particle size be between about 30 and 100 microns if the catalyst is to be used in a gas phase or slurry polymerization process and that a smaller particle size (less than 10 microns) be used if the catalyst is used in a solution polymerization.
Conventional porous metal oxides which have comparatively high surface areas (greater than 1 m2/g, particularly greater than 100 m2/g, more particularly greater than 200 m2/g) are preferred to non-porous metal oxides.
The xe2x80x9cdirectly fluoridedxe2x80x9d metal oxides used in this invention are prepared by directly treating the metal oxide with a source of fluoride. [By way of clarification, the present invention does not encompass the use of xe2x80x9cfunctionalized supportsxe2x80x9d which are taught in the aforementioned U.S. Pat. No. 4,536,484 and/or EP 906,920. In other words, the present invention eliminates the need for the pretreatment/functionalization which is required by the cited prior art.]
The term xe2x80x9cdirectly fluoridedxe2x80x9d is meant to broadly refer to the treatment of the metal oxide with a source of fluoride. Any inorganic or organic fluorine containing material which provides fluoride may be used. A review of these materials is given in the aforementioned U.S. Pat. No. 4,100,337 and the references cited therein. Exemplary sources of fluoride include HF, ammonium fluorides (such as NH4HF2 NH4BF4, (NH4)2SiF6) and alkali metal fluorides such as LiF, KF and NaF. The use of inorganic fluorides is preferred. The use of NaF is especially preferred. Conventional techniques to prepare the fluorided metal oxide may be used (as disclosed in the previously mentioned references). However, in a particular preferred embodiment of this invention, silica is simply contacted with an aqueous solution of fluoride at an acidic pH (as described further in the Examples). This is an inexpensive and convenient process with the further advantage that it does not produce waste byproducts which are expensive to handle or dispose of.
The amount of fluoridation agent present in the liquid is preferably from 0.1 to 20 weight % based on the weight of the silica. Alcohols or an aqueous alcohol solution may also be used in place of the water as the contacting liquid. Preferred contacting conditions include times from about 1 minute to about 3 days (especially from about 10 minutes to about 3 hours) at a temperature of from about 10xc2x0 C. to 200xc2x0 C. (under pressure) with particularly preferred temperatures being from about 20xc2x0 C. to 80xc2x0 C. After contacting the silica and sodium fluoride, the fluorided silica is removed from the liquid and preferably calcined prior to treatment with the aluminoxane.
Conventional calcining conditions may be employedxe2x80x94i.e. calcining temperatures of from about 150xc2x0 C. to about 900xc2x0 C. for periods of time ranging from about 10 minutes to about 48 hours. Preferred calcining conditions include temperatures of from 200xc2x0 C. to 700xc2x0 C. for times of from 1 to 8 hours.
The directly fluorided metal oxide used in this invention preferably has a fluorine content of from 0.01 to 15 weight % based upon the weight of the fluorine and metal oxide.
The fluorided metal oxide is preferably first contacted with an aluminoxane.
Aluminoxanes are readily available items of commerce which are known to be cocatalysts for olefin polymerization catalysts (especially group 4 metal metallocene catalysts). A generally accepted formula to represent aluminoxanes is:
(R)2 AlO(RAlO)m Al(R)2
wherein each R is independently an alkyl group having from 1 to 6 carbon atoms and m is between 0 and about 50. The preferred aluminoxane is methylaluminoxane wherein R is predominantly methyl. Commercially available methylaluminoxane (xe2x80x9cMAOxe2x80x9d) and xe2x80x9cmodified MAOxe2x80x9d are preferred for use in this invention. [Note: In modified MAO, the R groups of the above formula are predominantly methyl but a small fraction of the R groups are higher hydrocarbylsxe2x80x94such as ethyl or butylxe2x80x94so as to improve the solubility of the xe2x80x9cmodified MAOxe2x80x9d in aliphatic solvents.]
The directly fluorided metal oxide and aluminoxane are preferably contacted together using conventional techniques to prepare supported catalysts such as mixing the aluminoxane and fluorided metal oxide together in a linear or aromatic hydrocarbon (such as hexane or toluene) at a temperature of from 10 to 200xc2x0 C. for a time of from 1 minute to several hours. The amount of aluminoxane is preferably sufficient to provide from 1 to 40 weight % aluminoxane (based on the combined weight of the aluminoxane and the fluorided metal oxide). The intermediate product which is produced by these steps is a xe2x80x9csupported aluminoxanexe2x80x9d catalyst component. A catalyst molecule is then deposited on the supported aluminoxane. The catalyst molecule is a complex of a group 4 metal which is characterized by having at lease one phosphinimine ligand. Preferred catalyst are defined by the formula: 
wherein M is selected from titanium, hafnium and zirconium, L1 is a phosphinimine ligand; L2 is a ligand selected from the group consisting of a phosphinimine ligand, a cyclopentadienyl ligand which may optionally be substituted and heteroatom ligands; and L3 is an activatable ligand. It is preferred but n=2 (i.e. that there are two monoanionic activatable ligands). It is preferred that the metal M is titanium in the highest transition state (i.e. Ti4+). Detailed description of ligands L1, L2 and L3 are provided later.
It should also be noted that preferred catalyst systems according to this inventor are characterized by having a molar Al:M ratio (where Al represents the aluminum contained in the aluminoxane and M represents the group 4 metal) of from 10:1 to 200:1, especially from 50:1 to 150:1.
The catalyst component (i.e. the fluorided metal oxide/aluminoxane) may be combined with the polymerization catalyst using techniques which are conventionally used to prepare supported aluminoxane/metallocene catalysts. Such techniques are well known to those skilled in the art. In general, a hydrocarbon slurry of the catalyst component may be contacted with the catalyst complex. It is preferred to use a hydrocarbon in which the catalyst complex is soluble. The examples illustrate suitable techniques to prepare the xe2x80x9ccatalyst systemsxe2x80x9d of this invention.
Description of Ligands
L1 is a phosphinimine ligand (see A.1 below). L2 may be a phosphinimine ligand (see A.1), or a cyclopentadienyl ligand (see A.2), or a heteroatom ligand, (including a ketimide ligand, or a siloxy ligand, or an amido ligand, or an alkoxy ligand, or a boron heterocyclic ligand or a phosphole ligand (see part A.3.1 to A.3.6 below). Each L3 is an activatable ligand as described in Part A.4.
A. 1 Phosphinimine Ligand
Phosphinimine ligands are defined by the formula: 
wherein each R1 is independently selected from the group consisting of a hydrogen atom, a halogen atom, C1-20 hydrocarbyl radicals which are unsubstituted by or further substituted by a halogen atom, a C1-8 alkoxy radical, a C6-10 aryl or aryloxy radical, an amido radical, a silyl radical of the formula:
xe2x80x94Sixe2x80x94(R2)3
wherein each R2 is independently selected from the group consisting of hydrogen, a C1-8 alkyl or alkoxy radical, C6-10 aryl or aryloxy radicals, and a germanyl radical of the formula:
Gexe2x80x94(R2)3
wherein R2 is as defined above.
The preferred phosphinimines are those in which each R1 is a hydrocarbyl radical. A particularly preferred phosphinimine is tri-(tertiary butyl) phosphinimine (i.e. where each R1 is a tertiary butyl group).
A.2 Cyclopentadienyl Ligands
L2 may be a cyclopentadienyl ligand. As used herein, the term cyclopentadienyl ligand is meant to convey its broad meaning, namely a substituted or unsubstituted ligand having a five carbon ring which is bonded to the metal via eta-5 bonding. Thus, the term cyclopentadienyl includes unsubstituted cyclopentadienyl, substituted cyclopentadienyl, unsubstituted indenyl, substituted indenyl, unsubstituted fluorenyl and substituted fluorenyl. An exemplary list of substituents for a cyclopentadienyl ligand includes the group consisting of C1-10 hydrocarbyl radical (which hydrocarbyl substituents are unsubstituted or further substituted); a halogen atom, C1-8 alkoxy radical, a C6-10 aryl or aryloxy radical; an amido radical which is unsubstituted or substituted by up to two C1-8 alkyl radicals; a phosphido radical which is unsubstituted or substituted by up to two C1-8 alkyl radicals; silyl radicals of the formula xe2x80x94Sixe2x80x94(R1)3 wherein each R1 is independently selected from the group consisting of hydrogen, a C1-8 alkyl or alkoxy radical C6-10 aryl or aryloxy radicals; germanyl radicals of the formula Gexe2x80x94(R1)3 wherein R1 is as defined directly above.
It is preferred that L2 is cyclopentadienyl (optionally substituted) as illustrated in the examples.
A. 3 Heteroatom Ligands
As used herein, the term heteroatom ligand refers to a ligand which contains a heteroatom selected from the group consisting of nitrogen, boron, oxygen, phosphorus and sulfur. The ligand may be sigma or pi bonded to the metal. Exemplary heteroatom ligands include ketimide ligands, siloxy ligands amido ligands, alkoxy ligands, boron heterocyclic ligands and phosphole ligands. Brief descriptions of such ligands follow.
Phosphole ligands are also well known to those skilled in the art of olefin polymerization and are described as such in U.S. Pat. No. 5,434,116 (Sone, to Tosoh).
A.3.1 Ketimide Ligands
As used herein, the term xe2x80x9cketimide ligandxe2x80x9d refers to a ligand which:
(a) is bonded to the group 4 metal via a metal-nitrogen atom bond;
(b) has a single substituent on the nitrogen atom, (where this single substituent is a carbon atom which is doubly bonded to the N atom); and
(c) has two substituents (Sub 1 and Sub 2, described below) which are bonded to the carbon atom.
Conditions a, b, and c are illustrated below: 
The substituents xe2x80x9cSub 1xe2x80x9d and xe2x80x9cSub 2xe2x80x9d may be the same or different. Exemplary substituents include hydrocarbyls having from 1 to 20 carbon atoms; silyl groups, amido groups and phosphido groups. For reasons of cost and convenience it is preferred that these substituents both be hydrocarbyls, especially simple alkyls and most preferably tertiary butyl.
A.3.2 Siloxy Heteroligands
These ligands are defined by the formula:
xe2x80x94(xcexc)SiRxRyRz
where thexe2x80x94denotes a bond to the transition metal and p is sulfur or oxygen.
The substituents on the Si atom, namely Rx, Ry and Rz are required in order to satisfy the bonding orbital of the Si atom. The use of any particular substituent Rx, Ry or Rz is not especially important to the success of this invention. It is preferred that each of Rx, Ry and Rz is a C1-4 hydrocarbyl group such as methyl, ethyl, isopropyl or tertiary butyl (simply because such materials are readily synthesized from commercially available materials).
A.3.3 Amino Ligands
The term xe2x80x9camidoxe2x80x9d is meant to convey its broad, conventional meaning. Thus, these ligands are characterized by (a) a metal-nitrogen bond, and (b) the presence of two substituents (which are typically simple alkyl or silyl groups) on the nitrogen atom.
A.3.4 Alkoxy Ligands
The term xe2x80x9calkoxyxe2x80x9d is also intended to convey its conventional meaning. Thus these ligands are characterized by (a) a metal oxygen bond, and (b) the presence of a hydrocarbyl group bonded to the oxygen atom. The hydrocarbyl group may be a ring structure and/or substituted (e.g. 2,6 di-tertiary butyl phenoxy).
A.3.5 Boron Heterocyclic Ligands
These ligands are characterized by the presence of a boron atom in a closed ring ligand. This definition includes heterocyclic ligands which also contain a nitrogen atom in the ring. These ligands are well known to those skilled in the art of olefin polymerization and are fully described in the literature (see, for example, U.S. Pat. Nos. 5,637,659; 5,554,775 and the references cited therein).
A.3.6 Phosphole Ligands
The term xe2x80x9cphospholexe2x80x9d is also meant to convey its conventional meaning. xe2x80x9cPhospholexe2x80x9d is also meant to convey its conventional meaning. xe2x80x9cPhospholesxe2x80x9d are cyclic dienyl structures having four carbon atoms and one phosphorus atom in the closed ring. The simplest phosphole is C4PH4 (which is analogous to cyclopentadiene with one carbon in the ring being replaced by phosphorus). The phosphole ligands may be substituted with, for example, C1-20 hydrocarbyl radicals (which may, optionally, contain halogen substituents); phosphido radicals; amido radicals; silyl or alkoxy radicals.
A.4 Activatable Ligand
Each L3 is an activatable ligand. The term xe2x80x9cactivatable ligandxe2x80x9d refers to a ligand which may be activated by a cocatalyst or xe2x80x9cactivatorxe2x80x9d (i.e. the aluminoxane) to facilitate olefin polymerization. Exemplary activatable ligands are independently selected from the group consisting of a hydrogen atom, a halogen atom, a C1-10 hydrocarbyl radical, a C1-10 alkoxy radical, a C5-10 aryl oxide radical; each of which said hydrocarbyl, alkoxy, and aryl oxide radicals may be unsubstituted by or further substituted by a halogen atom, a C1-8 alkyl radical, a C1-8 alkoxy radical, a C6-10 aryl or aryloxy radical, an amido radical which is unsubstituted or substituted by up to two C1-8 alkyl radicals; a phosphido radical which is unsubstituted or substituted by up to two C1-8 alkyl radicals.
The number of activatable ligands depends upon the valency of the metal and the valency of the activatable ligand. As previously noted, the preferred catalysts contain a group 4 metal in the highest oxidation state (i.e. 4+) and the preferred activatable ligands are monoanionic (such as a halidexe2x80x94especially chloride, or an alkylxe2x80x94especially methyl). Thus, the preferred catalyst contains two activatable ligands. In some instances, the metal of the catalyst component may not be in the highest oxidation state. For example, a titanium (Ill) component would contain only one monoanionic activatable ligand. Also, it is permitted to use a dianionic activatable ligand although this is not preferred.
Polymerization Processes
The catalyst system of this meter is suitable for use in any conventional olefin polymerization process, such as the so-called xe2x80x9cgas phasexe2x80x9d, xe2x80x9cslurryxe2x80x9d, xe2x80x9chigh pressurexe2x80x9d or xe2x80x9csolutionxe2x80x9d polymerization processes. Polyethylene, polypropylene and ethylene propylene elastomers are examples of olefin polymers which may be produced according to this invention.
The preferred polymerization process according to this invention uses ethylene and may include other monomers which are copolymerizable therewith such as other alpha olefins (having from three to ten carbon atoms, preferably butene, hexene or octene) and, under certain conditions, dienes such as hexadiene isomers, vinyl aromatic monomers such as styrene or cyclic olefin monomers such as norbornene.
The present invention may also be used to prepare elastomeric co- and terpolymers of ethylene, propylene and optionally one or more diene monomers. Generally, such elastomeric polymers will contain about 50 to abut 75 weight % ethylene, preferably about 50 to 60 weight % ethylene and correspondingly from 50 to 25% of propylene. A portion of the monomers, typically the propylene monomer, may be replaced by a conjugated diolefin. The diolefin may be present in amounts up to 10 weight % of the polymer although typically is present in amounts from about 3 to 5 weight %. The resulting polymer may have a composition comprising from 40 to 75 weight % of ethylene, from 50 to 15 weight % of propylene and up to 10 weight % of a diene monomer to provide 100 weight % of the polymer. Preferred but not limiting examples of the dienes are dicyclopentadiene, 1,4-hexadiene, 5-methylene-2-norbornene, 5-ethylidene-2-norbornene and 5-vinyl-2-norbornene. Particularly preferred dienes are 5-ethylidene-2-norbornene and 1,4-hexadiene.
The polyethylene polymers which may be prepared in accordance with the present invention typically comprise not less than 60, preferably not less than 70 weight % of ethylene and the balance one or more C4-10 alpha olefins, preferably selected from the group consisting of 1-butene, 1-hexene and 1-octene. The polyethylene prepared in accordance with the present invention may be linear low density polyethylene having density from about 0.910 to 0.935 g/cc. The present invention might also be useful to prepare polyethylene having a density below 0.910 g/ccxe2x80x94the so-called very low and ultra low density polyethylenes.
The catalyst system of this invention is preferably used in a slurry polymerization process or a gas phase polymerization process.
The typical slurry polymerization process uses total reactor pressures of up to about 50 bars and reactor temperature of up to about 200xc2x0 C. The process employs a liquid medium (e.g. an aromatic such as toluene or an alkane such as hexane, propane or isobutane) in which the polymerization takes place. This results in a suspension of solid polymer particles in the medium. Loop reactors are widely used in slurry processes. Detailed descriptions of slurry polymerization processes are widely reported in the open and patent literature.
In general, a fluidized bed gas phase polymerization reactor employs a xe2x80x9cbedxe2x80x9d of polymer and catalyst which is fluidized by a flow of monomer which is at least partially gaseous. Heat is generated by the enthalpy of polymerization of the monomer flowing through the bed. Unreacted monomer exits the fluidized bed and is contacted with a cooling system to remove this heat. The cooled monomer is then re-circulated through the polymerization zone together with xe2x80x9cmake-upxe2x80x9d monomer to replace that which was polymerized on the previous pass. As will be appreciated by those skilled in the art, the xe2x80x9cfluidizedxe2x80x9d nature of the polymerization bed helps to evenly distribute/mix the heat of reaction and thereby minimize the formation of localized temperature gradients (or xe2x80x9chot spotsxe2x80x9d). Nonetheless, it is essential that the heat of reaction be properly removed so as to avoid softening or melting of the polymer (and the resultant-and highly undesirablexe2x80x94xe2x80x9creactor chunksxe2x80x9d). The obvious way to maintain good mixing and cooling is to have a very high monomer flow through the bed. However, extremely high monomer flow causes undesirable polymer entrainment.
An alternative (and preferable) approach to high monomer flow is the use of an inert condensable fluid which will boil in the fluidized bed (when exposed to the enthalpy of polymerization), then exit the fluidized bed as a gas, then come into contact with a cooling element which. condenses the inert fluid. The condensed, cooled fluid is then returned to the polymerization zone and the boiling/condensing cycle is repeated.
The above-described use of a condensable fluid additive in a gas phase polymerization is often referred to by those skilled in the art as xe2x80x9ccondensed mode operationxe2x80x9d and is described in additional detail in U.S. Pat. Nos. 4,543,399 and 5,352,749. As noted in the ""399 reference, it is permissible to use alkanes such as butane, pentanes or hexanes as the condensable fluid and the amount of such condensed fluid preferably does not exceed about 20 weight per cent of the gas phase.
Other reaction conditions for the polymerization of ethylene which are reported in the ""399 reference are:
Preferred Polymerization Temperatures: about 75xc2x0 C. to about 115xc2x0 C. (with the lower temperatures being preferred for lower melting copolymersxe2x80x94especially those having densities of less than 0.915 g/ccxe2x80x94and the higher temperatures being preferred for higher density copolymers and homopolymers); and
Pressure: up to about 1000 psi (with a preferred range of from about 100 to 350 psi for olefin polymerization).
The ""399 reference teaches that the fluidized bed process is well adapted for the preparation of polyethylene but further notes that other monomers may be employedxe2x80x94as is the case in the polymerization process of this invention.
Further details are provided by the following non-limiting examples.